The present invention relates generally to semiconductors, and, more particularly, to electronic fuse interconnect structures.
A fuse is a structure that is blown in accordance with a suitable electrical current. For example, an electrical current is provided through the fuse to eventually cause the fuse to blow and create an open circuit. Programming refers to intentionally blowing a fuse and creating the open circuit. In integrated circuitry memory devices, fuses can be used for activating redundancy in memory chips and for programming functions and codes in logic chips. Specifically, dynamic random access memory (DRAM) and static random access memory (SRAM) may employ fuses for such purposes.
Electronic fuses (e-fuses) can also be used to prevent decreased chip yield caused by random defects generated in the manufacturing process. Moreover, e-fuses provide for future customization of a standardized chip design. For example, e-fuses may provide for a variety of voltage options, packaging pin out options, or any other options desired by the manufacturer to be employed prior to the final processing. These customization possibilities make it easier to use one basic design for several different end products and help increase chip yield.
Some e-fuses take advantage of electromigration (EM) effects to blow and create the open circuit. For example, EM can be defined as the transport of material caused by the gradual movement of ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. In e-fuses that take advantage of EM effect, such transport of material caused by the gradual movement of ions can produce voids which cause the e-fuse to blow and create the open circuit.
However, in a typical vertical e-fuse EM may cause undesirable voids, thus creating the open circuit in undesirable locations. More specifically, vertical e-fuses comprise a via connecting an Mx metal to an Mx+1 metal, where the Mx+1 metal is generally positioned above the Mx metal. During programming, voids tend to form in the Mx metal due to EM, and eventually cause the vertical e-fuse to blow and create an open circuit at the Mx metal. An open circuit may be the desired result; however, causing the open circuit at the Mx metal may have undesirable results. An open circuit created by a void in the Mx metal may affect circuits other than the circuit targeted during programming of the e-fuse. These undesired open circuits may therefore decrease chip yield.
Also, the location of the void formation may affect the amount of current required to blow the e-fuse. Generally, higher currents may be required to form a larger void, therefore higher currents may be necessary to cause a void to form in the Mx metal as opposed to the via because the Mx metal may have a larger cross-sectional area than the via.